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Basics
Simple Rockets 2 is at its core, a physics and spaceflight simulator, where players can create and experiment with space and aircraft of their own creation. In this article we will discuss the basics of SimpleRockets 2 by giving a brief description of building and tweaking parts of your rocket and the basic terminology found in the game. Starting a New Build When starting a new build, a prompt will ask if you are building a rocket or a plane. This affects the orientation of your craft as well as how the autopilot functions. This can be changed by selecting the Command Pod and going to Part Properties. Every rocket must have at least 3 parts: A Command Pod (or Chip), Fuel Tank, and Engine. Command Pod The Command Pod is required for any craft you plan to have control over. It can be eliminated by using a Command Chip, useful for smaller craft like rovers, airplanes, or anything where the standard Pod would be out of place. To use a Command Chip you must place it somewhere on the craft, then select it and go to Part Properties, and select 'Set As Primary'. The Command Pod can then be deleted. Fuel Tank A fuel tank contains fuel for the engine to burn. Without it, your engine is a heavy, expensive paperweight. A fuel tank can be used for more than just fuel; they are the standard structural component in the game, useful for fuselages of planes and space stations or large ships, the standard crafting piece. All of the fuels that can be used will be discussed below. Engine Engines. The thing that makes the magic happen. Engines are (usually) attached directly below the fuel tank and burn fuel to generate thrust, although engines can be placed remotely by enabling the 'Fuel Line' modifier on every part in between the engine and it's tank. While there are default engines in the game, these are only preset designs; engine performances are procedurally generated based on the customization of each parameter and can be modified drastically to provide any desired output. Other Parts From there, there are dozens upon dozens of additional parts to use in building your craft. See the Part List for a full list of every part. Fuels There are 10 fuels that can be used in a fuel tank. Liquid Rocket Fuels * Kerolox - "Liquid oxygen and kerosene for use in rocket engines. It's cheap and only moderately cryogenic so it's safer and easier to work with. The downside is that it's not as efficient as some of the other fuels" - Kerolox is useful for launchers and first stages. It burns longer and does not require very large of a tank, but is quite heavy, making it impractical for orbital use. * Hydrolox - "Liquid oxygen and Liquid hydrogen for use in rocket engines. Hydrolox is very efficient, but it has extremely low density and therefore requires larger fuel tanks" - Hydrolox is ideal for orbital use. It produces almost the same thrust as Kerolox but weighs much less, allowing for a lower thrust (i.e. lower consumption) engine and otherwise much easier to push around in Zero-G. Due to its lower density, it burns quicker. * Methalox - "Liquid oxygen and liquid methane for use in rocket engines. Somewhat more efficient than kerolox, but easier to work with than hydrolox" - Methalox is a newer fuel type that is still being studied in real life and under testing. Useful for a more modern launcher or first stage Solid Rocket Fuels Full Article: Solid-Fuel Engines * Solid - "Solid fuel for use in rocket engines. It packs a lot of impulse into a small space, but it is heavy and expensive" - Useful for boosters, solid engines are simple and only good for one thing: making a ton of thrust. Once ignited, they burn at full power nonstop until it runs out of fuel. Nuclear Fuels Full Article: Nuclear Engines * Liquid Hydrogen - "Liquid hydrogen for use in rocket engines. Without the oxidizer the liquid hydrogen is even more efficient, but it can only be used in nuclear rocket engines" * Water - "Now that's what I call high-quality H2O" Other Fuels * Monopropellant - "Monopropellant is used by RCS nozzles for attitude control" * Xenon - "Xenon is used by ion engines. It's an inert gas, so it won't cause huge explosions. Depending on what you're going for that might be a good thing or a bad thing." - Used by ion engines which produce very little thrust but can burn nearly forever. * Battery - "Battery is used by gyroscopes, wheels, etc, and it can be recharged with solar panels" - Note that Command Pods contain a battery but a Chip does not, this can be used to give electrical power to a Chip powered vehicle or supplement a Pod vehicle. This is also required in an Ion engine. * Jet Fuel - "Special kerosene for use in Jet Engines" - Jet engines are used for atmospheric flight. Engine Tuning Engine Tuning is necessary to achieve the best performance for an engine's intended use. There is a great deal of science behind this (literally rocket science), but this article will give you a basic understanding of all the terminology and specifications. Tuning is done by selecting the engine and going to Part Properties. Open the Performance Analyzer. When designing an engine, it must be tuned for the altitude it will be run at, for optimal performance. The Altitude slider tells you the performance of the engine at the set altitude. Set it to around where the engine will see primary operation. The Rocket Engine section tells you info on the engine itself, while Staging Analysis takes into account available fuel and weight, among other factors, and how the stage functions together. When designing a stage, set it to just that stage. Thrust '- The force that the engine is pushing against the vehicle, in Kilonewtons. '''Isp '- Specific Impulse, or how much thrust is generated per the weight of fuel. In other words, the fuel efficiency. 'TWR '- Thrust-to-weight ratio. This is of the engine itself, to see the TWR of the whole stage, look at the Staging Analysis. 'Mass Flow '- Rate of fuel consumption in the engine. '''Exit Pressure - The pressure of the exhaust gases coming out of the rocket nozzle. Air Pressure - The atmospheric pressure at the altitude set by the slider. Delta V '''- How much additional velocity the stage can produce. This means that given every factor such as weight and fuel quantity, this stage can accelerate (or decelerate) the ship an additional 3,313m/s. '''Burn Time - How long the engine can run before the stage runs out of fuel. Starting and Ending TWR - When the fuel is full and the stage is heavier, it has a lower TWR, in this case 3.53. By the time the fuel is exhausted, it is significantly lighter and has a higher TWR of 13.43. Propellant Mass - The weight of fuel in the stage. Getting Into Orbit Let's discuss how all of this information applies to practical use, from the ground to orbit. When building a rocket, we need various stages not just because of fuel limitations, but because of performance limitations as altitude changes. Each stage of a rocket is designed to function for their respective altitudes. An engine designed to launch at sea level will perform very poorly in the vacuum of space, and vice versa. For a first stage, weight is not too important. What we care more about is raw thrust and how long we can make that thrust. That's why we might choose kerolox or methalox over hydrolox. A lower Isp is alright for a first stage, because this stage just needs to get the rocket as far away from the dense sea level as it can. The dense atmosphere requires a powerful combustion, provided by a high-pressure power cycle (Gas Generator or Staged) and a proper Nozzle Length. The Nozzle of a rocket engine expands the combustion gases, and having proper expansion is essential. The larger the nozzle, the more expansion there is, and the less exit pressure (think of putting your finger over a hose - the smaller hole results in higher exit pressure of the water). Top: Underexpanded. Exit Pressure is higher than Air Pressure (Nozzle too small). This is the least desirable and requires a larger nozzle. Note: In the vacuum of space, it will always be underexpanded. In this case you want the largest nozzle practical without it being too heavy. 2nd: Optimal. Exit Pressure and Air Pressure are equal. This provides the best performance, but given that a rocket climbs through the atmosphere rapidly, it will only spend a very brief amount of time in this phase. 3rd: Overexpanded. Exit pressure is lower than Air Pressure. A little bit of overexpansion is useful because as the rocket climbs to higher altitudes, the air pressure will decrease, eventually resulting in an Optimal expansion. Bottom: Grossly Overexpanded (Nozzle too large). This, along with underexpanded, reduce the efficiency of the engine, however Grossly Overexpanded will also make the rocket exhaust unstable. With this in mind, we must design our first stage so that the Exit Pressure is close or equal to the Air Pressure of sea level, where our rocket is launching from, in order to provide optimal efficiency of the engine. For the best lift-off performance, we will not want to overexpand it very much. Air pressure drops dramatically as you climb through lower altitudes, but in the upper atmosphere the change in pressure is much less dramatic. The point of the first stage is to get the rocket through those lower altitudes as fast as possible, so that our subsequent stages can operate at lower, and more consistent, atmospheric pressure. Note: For rockets using boosters, set the boosters to Optimal expansion at sea level, and overexpand the main engines. The boosters do the heavy lifting off the pad so we may trade some sea level performance of the main engines for higher altitude performance. Once it's time to utilize the second stage, we should be well above the ground and out of the most dense part of the atmosphere. The second stage will want to be a bit overexpanded because we are now off the ground and trying to gain velocity, making engine efficiency important (consider Hydrolox). As stated before, we didn't want to overexpand the nozzles of the first stage because lifting the big heavy rocket off the ground and getting it as high as possible is more important than efficiency. Let's say your first stage cuts out at 30km, and your second stage runs up to 70km. You will want to tune the Exit Pressure equal to an Air Pressure in the middle of the two altitudes. Experimentation is key, find what works for your specific build. The second stage should get you close to orbit. The third stage should operate in the vacuum of space and see very limited if any atmospheric use. This stage should establish your orbit. All of the heavy work of launch is over, so you will want to tune for lower thrust in exchange for Isp (efficiency) and switch to the lighter Hydrolox. This will result in a much lighter craft, which will offset the need for raw thrust. Just make sure you have enough Delta-V to establish orbit and you will be all set. Category:Tutorial Category:Information